Glossary

alpha

The transparency of an object (or pixel). If an object with a non-maximal
value of Alpha is placed over another object, the second object will
be visible under the first. In Inkscape, a value of Alpha of 255
means the object is completely opaque, while a value of 0 means it is
fully transparent (not visible).

Animated Portable Network Graphic (APNG)

An open standard for animated bitmap graphics,
the animated parallel of the PNG standard and
an alternative to MNG.
There is support for this format in Firefox 3
and Opera 9.5 but the PNG group has
rejected this extension to the standard.

Accessible Rich Internet Applications (ARIA)

An open standard for adding semantic content to web content. This
is important for accessibility to those with disabilities.
See: the WAI-ARIA
specification.

baseline

For text, the line on which most characters (i.e., “x”) rest. Some
characters such as “p” extend significantly below the
baseline. Other characters such as “O” usually extend a small
amount below the baseline so that they optically appear to rest on
the baseline. Inkscape can align text to a common baseline.
Inkscape also uses the word to describe the point at which
vertical text is aligned horizontally. The baseline is indicated
by a small square when text is selected.

bitmap graphics

The description of a drawing using pixels (in contrast to vectors).
Also refered to as “raster” graphics.

The smallest rectangular box with sides parallel to the x and y axis
that completely encloses an object.
Note: In Inkscape, the bounding box is calculated assuming
a round stroke
Join and
Cap
style if the stroke is visible and the Visual bounding
box option is selected in
the Tools section of the
Inkscape Preferences dialog. If the Geometric bounding
box option is selected, only the nodes are
considered in the calculation.

bump map

A bitmap graphics used to
define the contour of a surface so that a lighting effect can be
applied. The SVG specification uses the Alpha channel for this
purpose in several of the Filter primitives.
See: Wikipedia
entry.

Cascading Style Sheets (CSS)

A way of controlling the layout and style of graphics objects
(including text) through the use of external files. This allows
the separation of content from presentation. It allows documents
to be easily adapted for a variety of rendering methods such as
printing and web display.

A method for describing a color by the amount of cyan, magenta,
and yellow needed to generate the color. This subtractive color
model (where light is absorbed) is most often used in printing. As
a good black is difficult to obtain using a mixture of these
colors, a fourth ink, the Key or black, is
also used. See: Wikipedia entry.

dots per inch (dpi)

The number of pixels per inch when printing or displaying a
digitized image. Inkscape has a default resolution for
exporting bitmaps of 90 dpi.

ECMAScript

A standardized language typically used to manipulate elements in an HTML page.
See Wikipedia
entry. JavaScript is an implemenation of the ECMAScript
standard as is JScript used in Internet Explorer.

A correction factor to account for nonlinearity in
a display device. More technically, the numerical value
of the exponent of the power-law correction.

Gaussian distribution

Also called Normal
distribution, a mathematical function that
describes a distribution found often in statistics (e.g., the
distribution of scores on a test). The relevance for Inkscape
comes from the use of the distribution in the Gaussian Blur
filter. The key point is that the color of a pixel is determined
by the colors of nearby pixels in the source, weighting the
nearest pixels more.

A patented standard for compressing bitmap graphics supported by most
web browsers. The open PNG standard is technically superior and
should be the format of choice for lossless compressed bitmaps.

Graphics User Interface (GUI)

The interface a computer program presents to the user.

hexadecimal number

A way of representing a number using base 16 rather than the
normal base 10. Very commonly used with computers. The base 10
numbers 0–9 are augmented by the letters a through f (which may
or may not be capitalized) representing
the numbers 10–15. For example, 31 in base 10 is written as 1F
in hexadecimal (1 times 16 plus 15 is 31).

hue, saturation, lightness (HSL)

A method for describing a color using hue, saturation, and
lightness. See: Wikipedia
entry.

HyperText Markup Language (HTML)

The original markup language for web pages.
The current version is HTML 4.01. HTML5 will include inlined
SVG as part of the standard.
See: Wikipedia
entry.

Mathematical Markup Language.
An XML based language for marking up mathematical
notation. Permitted, along with SVG, in HTML5
documents.

Multipurpose Internet Mail Extensions (MIME)

An Internet standard originally developed for electronic mail
that assigns to each type of document content a unique name so
that clients (programs) can interpret the data correctly.

Multiple-Image Network Graphic (MNG)

An open standard for animated bitmap graphics,
the animated parallel of the PNG standard.
Unfortunately, there is little support for this
format in web browsers.

name spaces

The use of tags to define a region in a file where certain definitions are
applicable. For example, an XML file can contain both SVG and XHTML.
Name spaces keep the two from conflicting with each other.

opacity

The property of an object that determines the visibility of
an underlying object. Opposite of transparency.

Short for picture element. The smallest part of a digitized
image that includes all the color information for a
region. Computer screen resolutions are typically described as
having some number of pixels per inch. The pixel (px) is the
default user unit for SVG. Inkscape has a default
resolution for exporting bitmaps of 90 pixels/inch (ppi).
SVG viewers typically have a default resolution of either 72
or 90 ppi.

point

A unit derived from the days when printers used letters carved in
metal blocks for printing. Various points have been
defined. Inkscape uses the computer point, which is 1/72 of an
inch or 0.35277 mm.

Portable Network Graphic (PNG)

An open standard for compressing bitmap graphics supported by most
web browsers.

PostScript

A printing language created by Adobe. The language can be used
to describe a document in a device-independent way.
See: Adobe
PostScript site.

A method for describing a color using the amount of each primary
color present. See Wikipedia
entry.

red-green-blue-alpha (RGBA)

The addition of Alpha (transparency) as a fourth component to a
RGB specified color.

rubber band

The box drawn when click-dragging the mouse with the Select Tool
or the Node Tool active. The objects or nodes within the box
will be selected. The drag must begin over an area without an
object or with the Shift key held down.

A very common standard created by HP and Microsoft for defining
color use on monitors and printers. See
Wikipedia
entry. The basic property of this color space is that the
output intensity for a color (e.g., red) is (roughly) exponentially
dependent on the specified input value. All SVG colors are
defined using this standard. In SVG, color interpolation is by
default done in the sRGB space except for filters, which is by
default done in the linearRGB color space.

A language for authoring interactive audiovisual presentations.
See
Wikipedia entry.
SVG can uses SMIL for animation (in addition to JavaScript).

Tag Image File Format (TIFF)

A file format for storing high-quality images
such as photographs or line drawings.

tool tip

A short dialog shown while the mouse cursor is above some part of window.
A typical use is to describe the function of an icon.

transformation matrix

A 3 × 3 matrix that describes how an object is to be transformed.
The upper-left 2 × 2 sub-matrix controls scaling, rotating, and
skewing. While the upper-right 1 × 2 sub-matrix controls
translations, the bottom row is not modifiable.

An advantage of using transformation matrices is that cumulative
transformations can be described by simply multiplying the
matrices that describe each individual transformation. Inkscape
stores an object's transformation internally as a transformation
matrix (which can be seen and modified with the XML
Editor).

In non-matrix form, we have the transformation:
x' = Ax + Cy + E
and
y' = Bx + Dy + F
where (x', y') is the new coordinate of
a point at (x, y).

With the above set of equations, it is easy to see that E is
magnitude of a translation in the x direction
and F is magnitude of a translation in the y
direction. For scaling, A and D are the scale factors for the
x and y directions,
respectively. For a pure rotation, A = D = sin(theta) and B = −C
= cos(theta) where theta is the angle of the desired rotation.
For skewing, C and B control skewing parallel to the
x and y axes,
respectively.

A transformation matrix is always defined
with respect to some point. The internal representation is with
respect to the internal coordinate system origin (upper-left
corner of “page”).

transparency

The property of an object that determines the visibility of
an underlying object.

The length corresponding to the value one
after accounting for any transformations. SVG follows CSS and
defines that "1px" (one pixel) is equal to one user unit. It is
important to note that a CSS pixel is
not the same as a screen pixel.